Light valve projection systems have been in commercial use for many years and are capable of providing good performance. Over the years, a number of improvements have been made to enhance the performance of these systems. One such improvement is described in U.S. Pat. No. 4,283,120 issued to David A. Orser et al and assigned to the assignee of this application. One problem solved by the invention described in the patent was termed "burn-in" which produces a moire pattern of color, predominantly green, appearing within the projected picture. This problem is avoided by mounting a rotatable disk within the light valve housing so that its lower portion is immersed in a sump which holds the light modulating fluid causing the fluid to cover over at least one surface of the disk during the rotation of the disk. The raster is positioned on the disk offset from the coordinate axes with the origin at the disc center so that the movement of the fluid responsive to the disk rotation is along paths that intersect the diffraction gratings obliquely over the entire raster. Burn-in is eliminated because fluid motion never becomes tangential to either grating axis.
Recently, it has been observed that the viscosity of the fluid control layer in light valves operated with projected light flux densities greater than about 280 modulated lumens for color light valves and greater than about 750 modulated lumens for black and white light valves is more difficult to control than in those operated at lower light flus densities. In addition, light valve post mortem analyses of fluid related parameters show that a higher brightness condition is more severe than a standard brightness condition with regard to fluid degradation. The post mortem analyses on fluid, sorbents and disks from a variety of light valve types operated in the field and those on life test at higher brightness levels indicate accelerated degradation with respect to fluid related parameters. Life test data also show earlier failure for light valves operated at high brightness. Black and white light valves with higher light flux densities than color light valves have also been shown to exhibit similar accelerated degradation. One consequence of the current trend to higher brightness is that many light valve components including but not limited to the input window and lenticular lens are subjected to greater stress, induced primarily by increased temperatures and/or temperature gradients resulting from the higher light flux through the system.